check in the stditem.db the stats on the items need to be
small number - large number ie :
armour1
stats
ac 1-2 amc 1-2 dc 1-2 mc 1-2 sc 1-2
if you have it around the opposite way for example
ac 2-1 amc 2-1 dc 2-1 mc 2-1 sc 2-1 this will cause the wearer to be one hit killed by mobs i dont know why it happens lol but it just does, go through your standard items db and check the stats, the one hit bug can happen on all items not just armour that was just for an example